1. Field of the Invention
The invention relates generally to computer networks, and more specifically to a method and apparatus for presenting the image of a single node to a computer network for a computer center having a plurality of computers.
2. Description of the Prior Art
Terminals and intelligent workstations are generally linked to data centers, which may in turn be linked to other data centers. Thus, an end user may have access, not just to a local high performance computer system, but to high performance computer systems in data centers located throughout the world to provide access by geographically remote users to applications and data, as well as to permit workstation to workstation communication. Examples are found in banking, point of sale networks and the airline industry.
Such data centers (or computer centers) have fast growing computing and storage requirements. In some systems tens of thousands of users interact with the computer center and require thousands of transactions per second, while needing a response time of one or two seconds.
In order to provide maximum capacity and availability, a plurality of computer systems are often coupled together within a single data center. By coupling computers together, data processing jobs that require more capacity than that ordinarily available from the single most powerful computer in the data center can still be processed since the processing load can be distributed amongst a number of computers. Furthermore, the availability of multiple computers permits fault tolerance, since another system or computer can take over in the event of failure or other outage.
Existing coupling schemes provide various degrees of capacity and availability advantages over single system designs and, more importantly, provide the image of a single system to the program running in the system. Thus a program usually does not know or care which computer system it is running on.
Even though a complex of coupled computer systems may appear as a single system from the point of view of a program running within the complex, users accessing the complex from their terminals via a computer network still `see` a multiple system having separate computer systems. A user must `log` on to an individual one of several computer systems. This is a potential bottleneck to the user if the chosen system is overloaded or if it happens to fail.
Also, the failure to provide a single data center with a single node image to the network increases the complexity of the network. The multiplicity of processors in a data center should be transparent to the network but is not in existing networks.
In known networks, when a new computer is added to a data center, the network must be notified, and new network routes have to be defined using the new computer as a network node, thus generating network control traffic. Balancing the load on any particular processor in the data center must also then, involve the network, since processes controlling virtual circuits (sessions) would have to be relocated from an overloaded processor to an idle processor. If each processor, however, represented a different network node, then relocation of virtual circuits would involve their termination on one node and reactivation on another node (processor). Such relocation involves high network overhead and disruption. Avoidance of such relocation is desirable since it improves network performance.
There are a number of examples of such coupling already in existence including complexes of MVS systems under the control of the IBM Corp. JES2 or JES3 programs, complexes of UNIX systems coupled under the Locus system of UCLA and complexes using the IBM Corporation VM (virtual machine) system. These systems provide various degrees of capacity and availability improvement over that of a single system, and more importantly, in these systems a program usually doesn't "know" or "care" which computer system it is running on. The prior art, however, does not describe a system in which a complex of computers can appear to be a single node to a network connected to the complex.
The invention will now be described in an environment that is substantially based upon the IBM Systems Network Architecture (SNA). The invention, however, is not restricted to any specific type of network. A typical SNA network is described in the IBM manual "SNA Concepts and Products," IBM publication GC30-3072, and the IBM publication SNA Technical Overview, GC30-3073.
It is thus an object of the present invention to provide a system and method for attaching a complex of coupled systems to a network (or to multiple networks) such that these systems provide the image of a single network node to the network and, thereby, to the users accessing the complex via the network.
It is a further object to provide the network connection in such a way that the enhanced capacity and availability of the coupled complex is made available to the network.